The present invention relates to an apparatus and method for generating wavelength-tunable short optical pulses, and more particularly to an apparatus and method for generating wavelength-tunable short optical pulses on the order of femtosecond.
Until the present, generation of wavelength-tunable femtosecond optical pulses has been realized by use of a dye laser or a solid state laser. However, these lasers are relatively large apparatuses which require a large number of optical elements. Further, in such lasers, precise adjustment of the optical system must be performed in order to adjust the wavelength of generated pulses and to realize stable operation. Moreover, the variable range of wavelength is only about a few tens of nanometers, which is not sufficiently wide.
Recently, compact short-pulse lasers formed from optical fibers have been realized. However, as disclosed in Japanese Patent Application Laid-Open (kokai) No. 10-213827, conventional technical developments have attached importance to a manner of obtaining shorter optical pulses at a higher intensity and have failed to change the wavelength of output optical pulses.
P. Beaud et al. found that when short optical pulses are input to an optical fiber, new optical pulses are generated on the longer wavelength side [IEEE J. Quantum Electron., QE-23, p1938 (1987)).
However, the paper of P. Beaud et al. does not discuss the possibility of changing the wavelength of optical pulses. Further, since the authors used an ordinary fiber which is not a polarization-maintaining type, the output varied with time, and the obtained spectrum did not have a neat shape. Moreover, the efficiency of conversion from input energy to newly generated optical pulses was as low as about 45%, which is unsatisfactory.
Recently, parametric conversion using a nonlinear crystal has received a great deal of attention as a technique for conversion of wavelength of light. However, this method requires a very high pump light intensity. Further, since optical elements such as a crystal and mirrors must be adjusted in order to change the wavelength, handling of the apparatus is not easy.
An object of the present invention is to solve the above-described problem and to provide a compact apparatus and a method for generating wavelength-tunable short optical pulses, which apparatus and method can change the wavelength of generated pulses without adjustment of an optical system and enables generation of ideal femtosecond soliton pulses.
To achieve the above object, the present invention provides the following.
[1] An apparatus for generating wavelength-tunable short optical pulses, the apparatus comprising: a short-optical-pulse source; an optical characteristic regulation unit for regulating characteristics of light output from the short-optical-pulse source; and an optical fiber for receiving input pulses from the optical characteristic regulation unit and for changing the wavelength of output pulses linearly in accordance with the light intensity of the input pulses.
[2] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, wherein the optical characteristic regulation unit is a light intensity regulation unit.
[3] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, wherein the short-optical-pulse source is a femtosecond fiber laser.
[4] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, wherein the short-optical-pulse source is a picosecond fiber laser.
[5] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, wherein the optical fiber is a polarization-maintaining fiber.
[6] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, further comprising a nonlinear crystal connected to the optical fiber in order to generate short optical pulses of a different wavelength.
[7] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, further comprising four-wave mixing means for further converting the wavelength of generated optical pulses.
[8] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, further comprising an optical amplifier for amplifying optical pulses generated by the optical fiber.
[9] An apparatus for generating wavelength-tunable short optical pulses as described in [1] above, wherein the output pulses are ideal soliton pulses.
[10] An apparatus for generating wavelength-tunable short optical pulses as described in [2] above, further comprising means for electrically adjusting the light intensity regulation unit in order to control the wavelength of generated optical pulses.
[11] An apparatus for generating wavelength-tunable short optical pulses, the apparatus comprising: a short-optical-pulse source; a light intensity regulation unit for regulating the intensity of light output from the short-optical-pulse source; and an optical fiber for receiving input pulses from the light intensity regulation unit and for changing the wavelength of output pulses linearly, wherein the short-optical-pulse source, the light intensity regulation unit, and the optical fiber are assembled in the form of a portable apparatus.
[12] An apparatus for generating wavelength-tunable short optical pulses as described in [11] above, wherein the short-optical-pulse source is a femtosecond fiber laser.
[13] An apparatus for generating wavelength-tunable short optical pulses as described in [11] above, wherein the short-optical-pulse source is a picosecond fiber laser.
[14] A method for generating wavelength-tunable short optical pulses, the method comprising: regulating the intensity of light from a short-optical-pulse source; and inputting short pulses into an optical fiber in order to generate output pulses having a linearly varied wavelength.
[15] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the wavelength of generated output pulses is changed through a change in the length of the optical fiber.
[16] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the output pulses are passed through a nonlinear crystal in order to generate short optical pulses of a different wavelength.
[17] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the wavelength of generated optical pulses is further converted by means of four-wave mixing.
[18] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein optical pulses generated by the optical fiber are amplified by use of an optical amplifier.
[19] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein ideal soliton pulses are generated as the output pulses.
[20] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the light intensity regulation unit is adjusted electrically in order to control the wavelength of generated optical pulses.
[21] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the pulse width, spectral width, and center wavelength of the soliton pulses are varied through changing the waveform and spectral width of the input pulses.
[22] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein the wavelength and spectrum of the soliton pulses are varied through changing the direction of polarization of the input pulses.
[23] A method for generating wavelength-tunable short optical pulses as described in [14] above, wherein in addition to soliton pulses generated on the longer wavelength side, anti-Stokes pulses are generated on the shorter wavelength side as the output pulses.